Zoom lens and image pickup apparatus

Abstract

Disposing from an object side in the order of a positive first lens group which is fixed at the time of zooming, a negative second lens group which is moved at the time of zooming, an aperture stop, a positive third lens group which is fixed at the time of zooming, and a fourth lens group which is moved along the optical axis at the time of zooming to correct a change in image plane position arising from the zooming for focusing. The zoom lens is configured to simultaneously satisfy, when a focal length of the overall lens system at the telephoto end, an overall optical length, and an Abbe number of the second group first lens with respect to d-line are taken as ft, TL, and νd 21 respectively, conditional expressions (1): 0.62<TL/ft<0.88 and (2): 30<νd 21 <48.

What is claimed is: 
     
       1. A zoom lens, consisting of a first lens group which has a positive power and is fixed at the time of zooming, a second lens group which has a negative power and is moved along an optical axis at the time of zooming, an aperture stop, a third lens group which has a positive power and is fixed at the time of zooming, and a fourth lens group which is moved along the optical axis at the time of zooming to correct a change in image plane position arising from the zooming for focusing, disposed in this order from an object side, wherein:
 the first lens group is consisted of a first group first lens having a negative power, a first group second lens having a positive power, a first group third lens having a positive power, and a first group fourth lens having a positive power, disposed in this order from the object side; 
 the second lens group is consisted of a second group first lens having a negative power, a second group second lens having a negative power, a second group third lens having a positive power, and a second group fourth lens having a positive or negative power with at least one surface being aspheric, disposed in this order from the object side; and 
 the zoom lens is configured to simultaneously satisfy conditional expressions (1) and (2) given blow:
   0.62 <TL/ft <0.88  (1); and
 
   30<νd21<48  (2),
 
 
 
       where:
 ft is a focal length of the overall lens system at a telephoto end; 
 TL is a distance from an object side surface of the first group first lens to an image forming plane on the optical axis; and 
 νd 21  is an Abbe number of the second group first lens with respect to d-line, 
 wherein the second group second lens and second group third lens are cemented and the second lens group satisfies a conditional expression given below:
   1.89<Nd22  (18),
 
 
 
       where:
 Nd 22  is a refractive index of the second group second lens. 
 
     
     
       2. The zoom lens of  claim 1 , wherein the zoom lens satisfies a conditional expression (8) given below:
   17 <νd 11<27   (8),
 
 
       where:
 νd 11  is an Abbe number of the first group first lens with respect to d-line. 
 
     
     
       3. The zoom lens of  claim 1 , wherein the zoom lens satisfies a conditional expression (10) given below:
   0.17 <M 2 /ft <0.32   (10),
 
 
       where:
 M 2  is an amount of movement of the second lens group at the time of zooming from the wide angle end to the telephoto end. 
 
     
     
       4. The zoom lens of  claim 1 , wherein the zoom lens satisfies a conditional expression (11) given below:
   4.2 <f 3 /fw <8.0   (11),
 
 
       where:
 fw is a focal length of the overall lens system at the wide angle end; and 
 f 3  is a focal length of the third lens group. 
 
     
     
       5. The zoom lens of  claim 1 , wherein the third lens group consists of a third group first lens having a positive power with at least one surface being aspheric and a third group second lens having a negative power. 
     
     
       6. The zoom lens of  claim 1 , wherein an object side surface of the second group fourth lens is aspheric and an intersection between a vertical line drawn to the optical axis from an outermost edge of an effective area of the aspheric surface and the optical axis locates on the image plane side of an intersection between the aspheric surface and optical axis. 
     
     
       7. The zoom lens of  claim 1 , wherein the second group fourth lens is a plastic lens. 
     
     
       8. The zoom lens of  claim 1 , wherein the second group fourth lens satisfies a conditional expression (13) given below:
   10.0 <|f 24 /f 2|  (13),
 
 
       where:
 f 24  is a focal length of the second group fourth lens; and 
 f 2  is a focal length of the second lens group. 
 
     
     
       9. The zoom lens of  claim 1 , wherein the first group fourth lens simultaneously satisfies conditional expressions (14) and (15) given below:
   1.70 <Nd 14   (14); and
 
   42 <νd 14<58   (15),
 
 
       where:
 Nd 14  is a refractive index of the first group fourth lens with respect to d-line; and 
 νd 14  is an Abbe number of the first group fourth lens with respect to d-line. 
 
     
     
       10. The zoom lens of  claim 1 , wherein the first lens group satisfies a conditional expression (16) given below:
   75 <νd 1 m    (16),
 
 
       where:
 νd 1 m is an Abbe number of at least one positive lens in the first lens group with respect to d-line. 
 
     
     
       11. The zoom lens of  claim 1 , wherein the zoom lens satisfies a conditional expression (17) given below:
   0.25 <f 1 /ft <0.50   (17),
 
 
       where:
 f 1  is a focal length of the first lens group. 
 
     
     
       12. The zoom lens of  claim 1 , wherein the zoom lens satisfies a conditional expression (19) given below:
   0.25 <|f 2|/( fw·ft ) 1/2 <0.38   (19),
 
 
       where:
 f 2  is a focal length of the second lens group; and 
 fw is a focal length of the overall lens system at the wide angle end. 
 
     
     
       13. The zoom lens of  claim 1 , wherein the zoom lens satisfies a conditional expression (20) given below:
   1.30 <fw/IH <1.75   (20),
 
 
       where:
 fw is a focal length of the overall lens system at the wide angle end; and 
 IH is a maximum image height. 
 
     
     
       14. An image pickup apparatus, comprising the zoom lens of  claim 1 . 
     
     
       15. A zoom lens, consisting of a first lens group which has a positive power and is fixed at the time of zooming, a second lens group which has a negative power and is moved along an optical axis at the time of zooming, an aperture stop, a third lens group which has a positive power and is fixed at the time of zooming, and a fourth lens group which is moved along the optical axis at the time of zooming to correct a change in image plane position arising from the zooming for focusing, disposed in this order from an object side, wherein:
 the first lens group consists of a first group first lens having a negative power, a first group second lens having a positive power, a first group third lens having a positive power, and a first group fourth lens having a positive power, disposed in this order from the object side; 
 the second lens group comprises a second group first lens having a negative power, a second group second lens having a negative power, and a second group third lens having a positive power, disposed in this order from the object side; 
 the third lens group consists of a third group first lens having a positive power with at least one surface being aspheric and a third group second lens having a negative power; and 
 the zoom lens is configured to simultaneously satisfy conditional expressions (3),(4), and (9) given blow:
   0.62 <TL/ft< 0.88   (3) ;
 
   4.2 <f 3 /fw <8.0   (4); and
 
   30<νdp21<48  (9) ,
 
 
 
       where:
 ft is a focal length of the overall lens system at a telephoto end; 
 TL is a distance from an object side surface of the first group first lens to an image forming plane on the optical axis; 
 f 3  is a focal length of the third lens group; 
 fw is a focal length of the overall lens system at a wide angle end; and 
 νd 21  is an Abbe number of the second group first lens with respect to d-line. 
 
     
     
       16. The zoom lens of  claim 15 , wherein the zoom lens satisfies a conditional expression (8) given below:
   17 <νd 11<27   (8),
 
 
       where:
 νd 11  is an Abbe number of the first group first lens with respect to d-line. 
 
     
     
       17. The zoom lens of  claim 15 , wherein the zoom lens satisfies a conditional expression (10) given below:
   0.17 <M 2 /ft <0.32   (10),
 
 
       where:
 M 2  is an amount of movement of the second lens group at the time of zooming from the wide angle end to the telephoto end. 
 
     
     
       18. The zoom lens of  claim 15 , wherein the second lens group comprises a second group fourth lens with at least one surface being aspheric disposed on the image plane side of the second group third lens. 
     
     
       19. An image pickup apparatus, comprising the zoom lens of  claim 15 .